Observation of Transverse Polarization and Determination of Psionic Form Factors of the $\hat{I}›$ Hyperon at $\sqrt{s}=3.773$ GeV

Abstract

Using a data sample of $e^{+}{e}^{-}$ collision data corresponding to an integrated luminosity of 20.3 fb${}^{-1}$ collected by the BESIII detector at the BEPCII collider, we present an observation of transverse polarization and a complete determination of the psionic form factors of the $\hat{I}›$ hyperon in $e^{+}{e}^{-}\to \hat{I}›\bar{\hat{I}}›$ decay with the entangled $\hat{I}›-\bar{\hat{I}}›$ pair at $\sqrt{s}=3.773$ GeV. The relative phase between the psionic form factors is determined to be $\hat{I}”\hat{I}¦=(1.53\pm 0.36\pm 0.03)$~rad with a significance of 5.5 $\ddot{I}ƒ$ taking into account systematic uncertainty. This result indicates a non-zero phase between the transition amplitudes of the $\hat{I}›\bar{\hat{I}}›$ helicity states. Additionally, we measure the angular distribution parameter and the modulus of the ratio between the psionic form factors to be $\hat{I}\cdot =0.86\pm 0.05\pm 0.03$ and $R(s)=|G_E(s)/G_M(s)|=0.47\pm 0.08\pm 0.05$, where the first uncertainty is statistical and the second systematic.

9 pages, 5 figures, consistent with the publication in Phys. Rev. D (Letter) 112, L051102 (2025)